1. Field of the Invention
The present invention relates to a rechargeable battery. More particularly, the present invention relates to a rechargeable battery, a printed circuit board for the same and a method of fabricating the rechargeable battery.
2. Description of the Related Art
Recently, many types of high-capacity rechargeable batteries have been developed. Representative examples of widely-used rechargeable batteries include, e.g., nickel metal hydride (Ni-MH) batteries, lithium (Li) polymer batteries, and lithium ion (Li-ion) batteries. Rechargeable batteries are formed of a bare cell, or multiple bare cells, encased in a battery case, wherein each bare cell has electrodes, e.g., an anode and a cathode, and an electrolyte.
Rechargeable batteries may store a large amount of energy when in a charged state. Further, the rechargeable batteries may be capable of delivering the stored charge rapidly, i.e., they may be capable of a high current output. While desirable for the intended use, the presence of this large amount of stored energy may prove hazardous if the battery is mishandled or malfunctions.
During charging, the rechargeable battery is typically charged with energy from an external energy source, e.g., an external electrical supply. The external energy source may be capable of delivering large amounts of energy to the rechargeable battery in a short period of time. Thus, the recharging operation has the potential to generate hazardous conditions under certain circumstances. For example, if a charged rechargeable battery is short-circuited, or a short circuit occurs during charging, a large amount of the stored energy of the rechargeable battery may be output abruptly and rapidly. This can result in hazards such as fires or explosions.
In order to reduce the risk of such hazards, various safety devices may be provided for the rechargeable battery. When an abnormal current or voltage of the rechargeable battery is detected, e.g., due to an increase in temperature, excessive charging or discharging, etc., the safety devices can block the output of abnormal current from the rechargeable battery or otherwise prevent the development of dangerous conditions. As one type of the safety device, a separator or a vent may be provided to the bare cell of the rechargeable battery. Other types of safety devices may also be provided, external to the bare cell. For instance, a protective circuit may be provided external to the bare cell.
The protective circuit may be connected to at least one electrode terminal of the bare cell via one or more conductive members. The protective circuit may be configured to detect abnormal current or voltage and block the abnormal current or voltage, in order to prevent excessive charging or discharging of the battery. Other types of safety devices may also be provided, e.g., positive temperature coefficient (PTC) devices, fuses, bimetallic members, etc., which operate by reacting to excessive heat caused by abnormal current.
The bare cell and the safety device(s) may be enclosed in a case to complete the rechargeable battery. In some instances, the safety devices may be mounted on a printed circuit board (PCB), which may also include various other active and passive devices related to battery charging, monitoring, status, etc. The PCB may be physically bonded to the bare cell using, e.g., a resin, which is known as a hot melt method.
The PCB may be a multi-layered PCB, having the two major exterior surfaces formed of conductive layers and one or more interior conductive layers interleaved with a plurality of insulating layers. Conductive traces may be formed from the interior conductive layer, and conductive features such as contact terminals, bonding terminals, and conductive traces may be formed on the two exterior conductive layers. The contact terminals may be used for, e.g., making reversible contact between the board and an external charging apparatus, a portable electronic device, test probes, etc. The bonding terminals may be used for soldering various components to the PCB, e.g., wires, integrated circuit chips (ICs) and other active devices, passive devices such as resistors, etc. The bonding terminals may also be provided on the interior conductive layer, with the components being soldered thereto using through holes or blind vias.
Further details of a typical protective circuit and associated PCB will now be described. In general, an external contact terminal may be formed on an outer surface of the PCB. The external contact terminal may be exposed to the outside of the rechargeable battery case and may be used to, e.g., reversibly electrically connect the battery to an external energy source, e.g., an electric supply, electronic battery charger, etc., in order to charge the battery. The external contact terminal may be formed on a first surface of the PCB, i.e., an outer or exposed surface. The protective circuit may be mounted to a second surface of the PCB, i.e., an internal surface, so as to be enclosed in the battery case.
FIG. 1 illustrates a schematic plan view of an outer surface of a conventional rechargeable battery PCB, and FIG. 2 illustrates a schematic plan view of an opposite or inner surface of the PCB of FIG. 1. Referring to FIG. 1 the outer surface of the PCB 10 may include one or more exposed external contact terminals 20, which, as noted above, may be used to couple the battery to a charging apparatus. Referring to FIG. 2, the inner surface of the PCB 10 may include conductive features 30 and 40. Conductive features 40 may be, e.g., bonding terminals.
The external contact terminal 20 may be disposed on the outer surface of the PCB and may be exposed to the exterior of the rechargeable battery. To reduce the contact resistance between the external contact terminal 20 and an external apparatus in contact therewith, the external contact terminal 20 may be plated with, e.g., with gold or silver.
In order to plate the external contact terminal 20, a plating electrode of a plating power supply may be connected to the external contact terminal 20. However, if the plating electrode is placed in direct contact with the external contact terminal 20, a portion of the external contact terminal 20 under the plating electrode may not get plated, or uniform plating may be difficult to attain. Therefore, the conventional PCB 10 may utilize a plating lead-in line 22, which may extend across the outer surface of the PCB 10 from the external contact terminal 20. The plating electrode may then be coupled to the plating lead-in line 22 at some distance from the external contact terminal 20, thereby providing the necessary electrical connection to the external contact terminal 20 while avoiding marring the plating thereof.
In detail, a plurality of the plating lead-in lines 22 may be provided, each of which is connected to an external contact terminal 20. The plating lead-in lines 22 may be formed in a branch or tree pattern. That is, a main plating lead-in line may be provided for connection with the plating electrode, and the main plating lead-in line may then split or branch into a plurality of plating lead-in lines 22, each individually connected to an individual external contact terminal 20. The main plating lead-in line may be located in on a region of the surface of the PCB 10 that allows for connection with the plating electrode without affecting the plating of the external contact terminal 20. Additionally, before the plating process, some portions of the PCB 10 may be excluded from plating by covering them with a solder mask, such that they are protected from the plating solution, while the external contact terminal 20 and at least some of the plating lead-in line 22 is exposed, so as to be plated.
After the plating is complete, the plating lead-in line 22 tree structure may be sectioned by removing, e.g., cutting off, a portion of the PCB 10 that carries the lead-in lines. At least some portion of the tree structure may have to be removed in order to eliminate conductive pathways between the external contact terminals 20. Otherwise, short circuits will result from the plating lead-in lines 22 tying together multiple external contact terminals 20.
Finally, the resulting PCB 10 and the bare cell may be assembled and enclosed in the battery case. The PCB 10 and bare cell may be molded in the battery case so as to expose the external contact terminal 20.
A problem with the above-described approach is that portions of the plating lead-in lines 22 may not be completely removed. That is, referring to FIG. 1, portions of the plating lead-in lines 22 may not be completely removed from the PCB 10 and may remain around the external contact terminals 20. These remaining portions may give the external contact terminals 20 a defective appearance and/or cause short-circuits with adjacent conductive elements.
For example, in forming the rechargeable battery so that the external contact terminal 20 is exposed, the PCB 10 may be misaligned and some portions of the plating lead-in lines 22 may be exposed. Additionally, the portions of the plating lead-in lines 22 may be disposed next to the edge of the PCB 10, making them susceptible to short-circuits with conductive elements disposed adjacent to the PCB 10.